Surface science with nanosized particles in a carrier gas

The dynamics of nanoparticles in a carrier gas are governed by the physical and chemical nature of the surface. The total surface area can be divided into an "active'' and a "passive'' part. The active surface is the surface on which transfer of momentum, energy, and mass from the gas to the particl e takes place. The experiments show that the active surface may be determin ed in physically very different in situ experiments such as measuring the m obility b, the diffusion constant D, or the mass transfer coefficient K of the particle. The concept of the active surface manifests itself in scaling laws Kb = const, KD = const, and Yb = const, found valid over a large rang e of particle shapes and sizes. Y is the yield of low energy photoelectrons from the particles upon irradiating the carrier gas with light of energy b elow the ionization energy of the carrier gas molecules but above the photo electric threshold of the particles. While K, D and b are independent of th e chemical nature of the particles as far as we know today, the simultaneou s measurement of Y provides a chemical fingerprint of the particles and all ows one to observe, in combination with pulsed lasers as sources of light, the dynamical changes of the active surface while the nanoparticle is inter acting with the carrier gas. (C) 2001 American Vacuum Society. [DOI: 10.111 6/1.1339832].